original.html.erb

<% if local_assigns.include?(:phone) && local_assigns.include?(:location) %>
  <ul class="profile_info_triple">
    <li><%= link_to(fb_name(owner, :use_you => false, :linked => false), owner) %></li>
    <li><%= location %></li>
    <li class="phone"><%= phone %></li>
  </ul>
<% elsif local_assigns.include?(:phone) || local_assigns.include?(:location) %>
  <ul class="profile_info_dual">
    <li><%= link_to(fb_name(owner, :use_you => false, :linked => false), owner) %></li>
    <li class="phone"><%= phone %></li>
  </ul>
<% else %>
  <ul class="profile_info">
    <li><%= link_to(fb_name(owner, :use_you => false, :linked => false), owner) %></li>
  </ul>
<% end %>

test.html.erb

<% mode = 0 %>
<ul class="profile_info<%= yield :suffix %>">
  <li><%= link_to(fb_name(owner, :use_you => false, :linked => false), owner) %></li>
  <% if local_assigns.include?(:phone) %>
    <li class="phone"><%= phone %></li>
    <% mode += 1 %>
  <%end%>
  <% if local_assigns.include?(:location) %>
    <li><%= location %></li>
    <% mode += 1 %>
  <%end%>
</ul>
<% content_for :suffix {[ '', '_dual', '_triple' ][ mode ] } %>